1. Field of the Invention
The invention concerns a lever-type cam follower made of sheet metal, typically for a valve train of an internal combustion engine, said cam follower comprising two parallel side walls connected by a crossbeam, an underside of the crossbeam having a support for at least one gas exchange valve on one end, said support being limited by guide walls extending parallel to the side walls.
2. Field of the Invention
A generic cam follower of the pre-cited type is known from DE 100 30 341 A1. This cam follower is likewise made of sheet metal and is optimized with regard to its width and weight in the region of its valve stem support. However, despite all the measures proposed in this document, problems of design space can still be encountered during the installation of such a cam follower in the internal combustion engine. It is to be remarked further that, due to the undesired, still too large accumulation of mass at a distance from the fulcrum, the mass moment of inertia of the cam follower is also too high.
Particularly in the case of four-valve or five-valve structures, alone, or in conjunction with very compact cylinder spacing, it is clear to a specialist in the field of engine construction that a further optimization of the cam follower at least in the region of the valve shaft support is necessary in order to solve existing design space problems.
It is an object of the invention to provide a cam follower of the pre-cited type in which the mentioned drawbacks are eliminated by simple measures.
This and other objects and advantages of the invention will become obvious from the following detailed description.
The invention achieves the above objects by the fact that the one end of the cam follower is narrower than a rest of a length of the cam follower, and at least in a region of said one end, the side walls have a smaller mean wall thickness than over the rest of said length, which wall thickness increases at least in said region continuously from ends of the side walls in direction of the crossbeam. A thickness of the guide walls may be smaller than, or substantially equal to the mean wall thickness in said region of said one end.
The cam follower thus obtained is therefore further optimized with regard to its design space requirement. In the final analysis, the minimum width of the cam follower in the region of the valve stem support is determined by the thickness of the valve stem and the thickness of the adjoining guide walls of the cam follower on both sides, or, in other words, by the distance between the outer surfaces of the side walls in this region.
Due to the narrow configuration of the cam follower at the one end, in conjunction with the fact that, to put it simply, the guide walls are thinner than the side walls, the mass moment of inertia of the cam follower is further reduced and its design space requirement, at least in the region of the valve stem support, is distinctly smaller than in prior art cam followers. At the same time, the cam follower has a particularly rigid configuration, and if the region of its valve stem support is made by a stamping and extrusion molding method, it also possesses an excellent strength in this region. Further, due to the continuously increasing thickness of the side walls, at least in the region of the one narrow end, creases in the transition region to the crossbeam are effectively prevented.
It is clear that, depending on each particular case of use, a person skilled in the art will vary the height of the guide walls so as to prevent a slipping-off of the cam follower during assembly and during the start-up phase of the internal combustion engine.
The valve stem support is advantageously made by the aforesaid stamping and extrusion molding method i.e., by cold forging, in the same or similar manner as described in the initially cited document DE 100 30 341 A1. For xe2x80x9cthinning-outxe2x80x9d the guide walls, material from their outer surfaces is also used. This is done after the side walls have been bent and, if necessary, with the use of a partially thickened blank. The sheet metal cam follower, as such, can be made out of strip or solid material. The most preferred material is sheet steel but it is also conceivable to use other sheet metals with which a person skilled in the art is familiar.
According to a further embodiment of the invention, the narrow one end of the cam follower is formed out of a gradually tapering portion of the cam follower. From the fabrication point of view, this embodiment is simple to realize and prevents cracking in the transition region. However, it is also possible to make the narrow end as a stepped shoulder.
According to a further advantageous feature of the invention, the narrow one end ends in a longitudinal portion of uniform width so that the guide walls extend parallel to the outer surfaces of the side walls. This is advantageous from the fabrication point of view. However, it is also possible to let the narrow one end taper to a point. A person skilled in the art will use appropriate calculation methods to optimize the length of the narrow portion of the cam follower and make the guide walls, and the side walls in the region of the guide walls, as narrow as possible till an optimum light-weight structure is obtained in this region which, at the same time, possesses adequate rigidity etc.
According to a particularly important feature of the invention, the guide walls are made integrally with the underside of the crossbeam and extend away from this, and further, the outer surfaces of the guide walls are clearly offset inward from the outer surfaces of the side walls in the region of the one end. It is therefore clear that the guide walls are made out of the material of the bottom and also quite obvious that they are not to be considered as extensions of the side walls. As already elucidated above, this is advantageous from the fabrication and design space point of view.
Alternatively, however, the guide walls may also be made as separate components that, at least, originally do not start from the underside of the crossbeam. If the guide walls are made as separate elements, they can be fixed on the underside by appropriate fixing methods such as welding, gluing or positive retention.
The proposed cam follower is preferably made of a light-weight material such as sheet metal but it is also conceivable to make a cam follower having the design of the invention by creative forming or casting.
The invention will now be described more closely with reference to the appended drawings.